1. Field of the Invention
The present invention relates to composite ceramic substrates, and more specifically, relates to composite ceramic substrates having built-in circuit elements and having laminated ceramic substrates and resin layers.
2. Description of the Related Art
Conventional technologies in this field include a laminated electronic component disclosed in Japanese Unexamined Patent Application Publication No. 9-186042 (Patent Document 1) and a high-frequency semiconductor device disclosed in Japanese Unexamined Patent Application Publication No. 2003-124435 (Patent Document 2).
The laminated electronic component disclosed in Patent Document 1 is formed by laminating a plurality of insulating sheets so as to interpose a circuit element therebetween and to define a laminate having opposing main surfaces and side surfaces connecting the main surfaces, preparing a plurality of external electrodes on the outer surfaces of the laminate so as to be electrically connected to the circuit element, and forming a recess at least at the central portion of a surface at a circuit board side of the laminate when the laminated electronic component is mounted on the circuit board via the external electrodes. With such a recess formed on the surface at the circuit board (specifically, a flexible printed-circuit board) side of the laminate, even if the circuit board is bent, the bent surface of the printed-circuit board does not come into contact with the surface of the circuit board side of the laminate. Therefore, the pressing-up force against the laminate is avoided. Thus, detachment of the laminate from the printed-circuit board and breakage of the laminate are prevented.
The high-frequency semiconductor device disclosed in Patent Document 2 includes a composite resin material layer provided on the bottom of a ceramic substrate. The composite resin material layer is made of an epoxy resin and an inorganic filler material and has a flat bottom on which electrodes for external connection are provided. Semiconductor elements and passive components, which are connected to the ceramic substrate, are embedded in the inside of the composite resin material layer. With such a structure, the bottom surface of the board can be used as a mounting area to improve the mounting density. Furthermore, mechanical properties and reliability in moisture resistance are improved by embedding the semiconductor elements and the passive components in the composite resin material layer.
The laminated electronic component disclosed in Patent Document 1 avoids the pressing-up force by forming the recess at the central portion. However, the entire laminate bends corresponding to bending of the printed-circuit board. It is not a problem when surface-mounted components are not mounted on the top surface or on both top and bottom surfaces of the laminate. However, when the surface-mounted components, such as passive components and active components, are mounted on the laminate, these surface-mounted components cannot correspond to the bending of the laminate, which may cause disconnection of terminals for external connection of the surface-mounted components from the electrodes on the surface of the laminate. Thus, breaking of the wires may occur.
In the high-frequency semiconductor device disclosed in Patent Document 2, the size of the board component can be decreased by mounting the surface-mounted components, such as active components and passive components, on the bottom or top surface of the ceramic substrate. However, the ceramic substrate also bends corresponding to the bending of the printed-circuit board. Therefore, since the surface-mounted components cannot correspond to the bending of the ceramic substrate, the terminals for external connection of the surface-mounted components are disconnected from the electrodes on the surface of the laminate, which causes breaking of the wires as in the case of the laminated electronic component of Patent Document 1.